This invention relates to an elevator control apparatus. More particularly, it relates to an elevator control apparatus actuated at the start of an elevator cage under the condition that an electromagnetic brake is reliably operating.
FIG. 9 is a schematic view showing the construction of a conventional elevator system As shown in the figure, the elevator system comprises a common rotary shaft 1, on which a motor 2, a wheel to be braked 3 and a sheave 4 are mounted at suitable intervals. The motor 2 is electrically connected with a motor drive circuit 5, which in turn is connected to a three-phase A.C. power source 7 through the contact 6 of an electromagnetic contactor (not shown). An electromagnetic brake 8 is constructed of a lining 9 which grasps and brakes the wheel to be braked 3, a plunger 10 which is attached to the lining 9, a compression spring 12 which is interposed between the plunger 10 and a base 11, a switch 13 which turns on or off in coordination with the movement of the plunger 10, and a coil 14 which is wound round the plunger 10. Owing to the force of the spring 12, the electromagnetic brake 8 brakes the wheel to be braked 3 by means of the lining 9 through the plunger 10. When the coil 14 is energized by a brake control circuit 15, the plunger 10 is attracted and overcomes the urging force of the spring 12, thereby to separate the lining 9 from the wheel to be braked 3 and to releasing the braking of the wheel. Wound round the sheave 4 is a rope 16, one end of which has an elevator cage 17 coupled thereto and the other end of which has a counterweight 18 coupled thereto.
In starting the elevator cage 17, the aforementioned contact 6 and the contact 19a (in FIG. 10 to be referred to below) of the brake control circuit 15 are closed, whereby the braking by the electromagnetic brake 8 is released, and electric power for generating torque is supplied from the power source 7 to the motor 2 by the motor drive circuit 5.
FIG. 10 is a circuit diagram of the brake control circuit 15 shown in FIG. 9. Contact 19a of an electromagnetic contactor (not shown) which is closed at the start of the elevator cage 17 but which is open when the cage 17 is stopped contact 13a of the aforementioned switch 13, and coil 14 are connected in series with one another across the plus (+) and minus (-) sides of a power source (not shown). Contact 13a is in a closed state in order to connect the coil 14 directly to the power source for the reason that, until the plunger 10 is attracted upon the energization of the coil 14 of the electromagnetic brake 8, the coil 14 requires a great current for overcoming the urging force of the spring 12. Subsequently, once the plunger 10 has been attracted, contact 13a falls into an open state because the attracted state of the plunger 10 can be maintained even with a decreased coil current. At this time, a current limiting resistor 20A connected in parallel with the contact 13a is operatively connected to the coil 14, whereby the current flowing through this coil is decreased. A resistor 20B connected in parallel with the coil 14 is a coil protecting resistor by which electromagnetic energy stored in the coil 14 is absorbed when the coil current is cut off.
In starting the elevator cage 17, the electromagnetic contactor contact 19a is closed, and the coil 14 of the electromagnetic brake 8 is connected to the power source through the switch contact 13a as well as the electromagnetic contactor contact 19a. Thus, the coil 14 is energized to attract the plunger 10, so that the lining 9 releases the braking of the wheel to be braked 3. The motor 2 begins to rotate, and the elevator cage 17 starts smoothly. Since, at this time, the contact 13a of switch 13 interlocked with the plunger 10 opens, the coil current flows from the plus (+) side of the power source to the minus (-) side thereof via the electromagnetic contactor contact 19a, current limiting resistor 20A and coil 14, and the current flowing through the coil 14 is limited by the current limiting resistor 20A. As a result, the generation of heat by coil 14 is suppressed, and the consumption of electric power in the coil 14 is also suppressed.
In the operation of the above-described elevator control apparatus when the elevator cage is to be started, the motor sometimes generates torque while the braking force of the brake is still acting. In this case, the moment the brake has been completely released and the braking force disappears, the elevator cage is abruptly accelerated, and the riding quality of the cage is impaired. Moreover, since the switch contact of the brake control circuit is a mechanical contact, inferior touch is intrisically liable to occur, and inferior touch ascribable to the improper adjustment of the contact is also liable to occur. Therefore, the coil current is already limited during the attraction of the plunger Accordingly, the motor might rotate with the plunger held unattracted, namely, with the lining touching the wheel to be braked. In such a situation, abnormal wear of the lining, etc. will occur, and the brake will fail to work, and cause a serious accident. Therefore, the inspection of the switch contact is always required, and the maintenance of the contact is laborious.